Adding SI prefixes creates multiples and submultiples; however, as the unit is squared, the order of magnitude difference between units doubles from their comparable linear units. For example, a kilometre is one thousand times the length of a metre, but a square kilometre is one million times the area of a square metre.

A square metre is not the same as a metre square,[2] an area 2 metres wide by 5 metres long would be 10 square metres. In contrast, a 10-metre square (10 metres by 10 metres) is actually 100 square metres.